The overall goal of this project is to understand the role of the oncogenic and tumor survival pathways, Mek/Erk, JAK/STAT3 and PI3K/Akt in breast oncogenesis and to develop new strategies for more effective breast cancer treatment. The receptor tyrosine kinase ErbB2 is overexpressed in human breast cancer and this is associated with poor prognosis. ErbB2 heterodimerizes with ErbB1(EGFR), ErbB3 or ErbB4 and stimulates many signal transduction pathways leading to the constitutively activated Akt, STAT3 and Erkl/2 in breast cancer. It remains; however, unclear which of these pathways are most important for maintaining malignant transformation. Furthermore, the contribution of Mek/Erk, JAK/STAT3 and PI3K/Akt pathways to breast oncogenesis and treatment outcome is not known. We and others have developed disrupters of these signaling pathways including antibodies to ErbB2 and inhibitors of ErbB1 tyrosine kinase, Mek and PI3K kinases, JAK/STAT3 signaling and farnesyltransferase, an enzyme required for the activation of farnesylated proteins such as Ras which activates Mek/Erk and PI3K/Akt pathways. In this project we propose to test the hypothesis that constitutively activated Mek/Erk, JAK/STAT3 and/or PI3K/Akt pathways contribute to breast oncogenesis and tumor resistance, and that targeted intervention of these pathways blocks malignant transformation, induces apoptosis and sensitizes breast tumors to chemotherapy. This hypothesis will be tested through the following specific aims: 1) To investigate the role of constitutively activated PI3K/Akt, JAK/STAT3 and Mek/Erk, in breast cancer oncogenesis. Here we will determine if genetic and pharmacological disruptions of these pathways reverse malignant transformation and induce apoptosis. Dominant negative forms of PI3K, Akt, Mek, STAT3 and Ras will be used. Pharmacological inhibitors of JAK/STAT3 pathway, PI3K, Mek and farnesyltransferase will also be used individually or in combination. 2) To determine if resistance to Herceptin or Iressa of ErbB2 and/or EGFR overexpressing breast cancer cells is due to constitutively activated Akt/PI3K, JAK/STAT3 and/or MEK/Erk pathways. To this end, we will determine if inhibitors of these pathways sensitize breast cancer cells to Herceptin and/or Iressa. 3) To determine if resistance of breast cancer cells to Adriamycin, cyclophosphamide and/or taxotere could be overcome by targeted pharmacological intervention of PI3K/Akt, Mek/Erk and/or JAK/STAT3 pathways. 4) To conduct a hypothesis-driven phase I/lI clinical trial of preoperative Adriamycin (A), cyclophosphamide (C) and FTI R115777 (Zarnestra) in patients with locally advanced breast cancer and metastatic breast cancer. Here we will determine if pre-treatment levels of ErbB1, ErbB2, ErbB3 and/or ErbB4, and phosphorylated levels of Akt, STAT3 and/or Erkl/2 predict clinical response to AC/FTI. We will also correlate clinical response to ability to suppress protein farnesylation and the levels of phospho Akt, phospho Erkl/2 and/or phospho STAT3. Results from these studies will enhance our understanding of the role of Mek/Erk, JAK/STAT3 and PI3K/Akt pathways in breast cancer oncogenesis and treatment outcome and will result in improved therapies of human breast cancers.